Pattern-abradable/abrasive coatings for steam turbine stationary component surfaces

ABSTRACT

A pattern-abradable seal assembly is provided for a stationary steam turbine component. The seal assembly, in use, is oriented in opposition to at least one seal tooth on a rotatable turbine component so as to inhibit leakage flow across the seal assembly in one direction, the seal assembly may include an annular seal carrier having at least one axially-oriented surface; a pattern-abradable/abrasive seal coating or insert at least partially covering the at least one axially-oriented surface, the pattern-abradable/abrasive seal coating having a pattern formed thereon adapted to face and be at least partially penetrated by the at least one seal tooth. A plurality of anti-swirl elements project radially beyond the pattern and are arranged to provide at least an axial component of flow across the abradable seal assembly. The coating or insert may also be used on other stationary turbine component surfaces to direct flow in a predetermined direction.

BACKGROUND

The invention relates to pattern-abradable/abrasive seals in steamturbines and especially to abradable/abrasive coatings with patterns inthe shape of sealing features, anti-swirl and/or guide seal featuresdisposed radially outwardly of shrouded nozzle/buckets or on surfaces onstationary components axially adjacent to the nozzles/buckets to reduceleakage flow, reduce swirl and/or to aerodynamically guide the leakageflow to improve turbine efficiency.

It is well known to use abradable/abrasive materials which readily formseals between fixed and rotating parts of a turbine, whereby therotating part erodes a portion of the fixed abradable material to form aseal having a very close tolerance. An important application ofabradable seals in steam turbines where a rotor supporting a pluralityof wheels, each of which mounts a plurality of blades or bucketsrotating within a surrounding shroud. Utilizing abradable seals tominimize the clearance between the blade tips/nozzle root location andinner wall of the opposed shroud, makes it possible to reduce leakage ofthe working fluid which could be steam, across the blade tips andthereby enhance turbine efficiency.

Similar abradable/abrasive seals are also employed in turbines along theturbine rotor section to minimize leakage flow along the rotor shaftbetween higher and lower pressure regions. For example, conventionallabyrinth seals provide a torturous path along the rotor shaftminimizing leakage flow, and generally, comprise a plurality of radialteeth extending from the rotor, with a small cold clearance between theteeth and the opposed, stationary abradable seal.

Typically, metal or ceramic abradable seals are spray-coated onto thestationary seal surface, and are effective to establish a radialclearance of about 15 mils.

There is a continuing need to improve efficiency by further reducingclearances, guiding the leakage flow at a favorable angle to adjacentnozzle/buckets and by minimizing the effect of swirl or tangential flowat the seal caused by the rotating component which decreasesreliability, turbine efficiency and thus turbine performance.

BRIEF SUMMARY OF THE INVENTION

Accordingly, in one exemplary but nonlimiting embodiment, there isprovided a pattern-abradable/abrasive seal assembly for a stationarysteam turbine component, the seal assembly, in use, oriented inopposition to at least one seal tooth on a rotatable steam turbinecomponent so as to inhibit leakage flow across the seal assembly and/orguide the leakage flow in a first direction, the seal assemblycomprising an annular seal carrier having at least one axially-oriented,annular seal surface; a pattern-abradable/abrasive seal coating at leastpartially covering the at least one axially-oriented, annular sealsurface, the pattern-abradable/abrasive seal coating having a patternformed therein, adapted, in use, to face and be at least partiallypenetrated by the at least one opposed seal tooth; and a plurality ofanti-swirl elements projecting radially beyond the pattern and arrangedcircumferentially about the at least one axially-oriented, annular sealsurface.

In another exemplary but nonlimiting embodiment, there is provided acoating or insert for use on a surface of a stationary steam turbinecomponent located along the steam path comprising: a first surfacefacing an adjacent rotating steam turbine component; and a firstpattern-abradable/abrasive coating or insert having a pattern formedtherein applied to the surface wherein the pattern is designed to directleakage flow in a predetermined direction relative to the stationarysteam turbine component.

In still another exemplary but nonlimiting embodiment, there is provideda turbine bucket and abradable seal assembly comprising a bucket havinga tip shroud formed with plural radially-directed seal teeth; astationary stator component surrounding the bucket and having pluralabradable seals opposing respective ones of the plural radially-directedseals teeth; wherein each of the plural abradable seals includes anabradable seal coating having a pattern formed on a surface thereoffacing a respective one of the plural, radially-directed seal teeth, andat least one an anti-swirl element projecting radially beyond thepattern and arranged to provide at least an axial component of flowacross the seal assembly, the at least one anti-swirl element opposed toone of the plural radially-directed seal teeth, and adapted to be atleast partially penetrated thereby.

The invention will now be described in detail in connection with thedrawings identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side elevation of a shrouded steam turbine bucketinteracting with pattern-abradable seal elements on a radially opposedstationary stator component and on adjacent upstream and downstreamnozzles;

FIGS. 2-5 illustrate various surface patterns that may be employed onthe surface of the seal elements shown in FIG. 1;

FIGS. 6-8 illustrate an exemplary but nonlimiting embodiment of apattern-abradable seal and an opposed seal tooth;

FIGS. 9-11 illustrate an exemplary but nonlimiting embodiment of ananti-swirl feature incorporated into the patterned-abradable seal;

FIGS. 12-14 illustrate a second exemplary but nonlimiting embodiment ofan anti-swirl elements added to a patterned-abradable seal;

FIGS. 15-17 illustrate a different surface patterns that may be employedon the surface of the seal added to a pattern-abradable seal;

FIGS. 18-20 illustrate a third exemplary but nonlimiting embodiment ofanti-swirl elements added to a pattern-abradable seal;

FIGS. 21-23 illustrate a fourth exemplary but nonlimiting embodiment ofanti-swirl elements added to a pattern-abradable seal;

FIG. 24 is a partial side elevation of a shrouded bucket tip andpattern-abradable/abrasive seals on a radially outward stationary statorcomponent and on a stationary downstream nozzle in accordance withanother exemplary but nonlimiting embodiment of the invention;

FIG. 25 illustrates a nozzle root seal arrangement incorporatingpattern-abradable seals in accordance with another exemplary butnonlimiting embodiment of the invention;

FIG. 26 discloses pattern-abradable seals incorporated in a packing ringsegment in accordance with another exemplary but nonlimiting embodimentof the invention; and

FIG. 27 is a plot showing a reduction in tangential velocity as afunction of length of an anti-swirl element on a pattern-abradable sealin accordance the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference initially to FIG. 1, a shrouded bucket 10 is shownmounted to a rotor wheel (not shown) axially between a pair of upstreamand downstream nozzle vanes 12, 14. The shrouded bucket 10 is providedwith a tip shroud 16 formed with a plurality of radially-projecting,axially-spaced teeth 18, 20 and 22, each of which is arranged tointeract with a respective seal element 24, 26 and 28 on the surroundingstator or stator shroud 30 (sometimes referred to herein as a “sealcarrier”). The seal elements are fixed to stator seal surfaces 32, 34and 36, respectively. The seal elements are identical and, therefore,only one need be described in detail. Thus, for example, the seal 26 isa pattern-abradable seal that may be spray coated on the adjacent statorseal surface 34, and may comprise an abradable metallic or ceramicmaterial typically used for such purposes.

More specifically, an abradable coating can be applied by thermalspraying, e.g., by plasma spraying the coating composition through amask onto the stator shroud surface 34. Exemplary methods of producingan abradable coating on a substrate, utilizing, for example, anabradable ceramic coating composition, is described in commonly-ownedU.S. Pat. No. 6,887,528.

Exemplary but non-limiting abradable patterns for the coating that formsthe seal 26 are illustrated in FIGS. 2-5. It will be appreciated thatthese patterns are not drawn to scale but are enlarged for clarity. Morespecifically, FIG. 2 illustrates a pattern comprised of angled, spacedand staggered “bricks” 38. The “bricks” are arranged in circumferentialrows, with one row staggered circumferentially relative to the other.Note that the angled orientation of the pattern will also serve to guidethe leakage flow in a desired path relative to a downstream component.FIG. 3 illustrates a dense, circumferentially staggered-brick pattern,with the bricks 40 arranged substantially perpendicular to the flowdirection. FIG. 4 illustrates a diamond-mesh pattern 42, and FIG. 5illustrates a staggered chevron pattern 44. In all cases, adjacentannular rows of similar pattern elements are circumferentially offset orstaggered. It will be appreciated that other patterns are also withinthe scope of the invention.

Typically, the rotating bucket teeth will penetrate from about 50 toabout 100 percent of the seal thickness. For example, with a tight coldradial clearance between the bucket teeth 18, 20, 22 and the statorshroud 24, 26, 28 of about 15 mils, the abradable coating with athickness of about 30-100 mils, may be penetrated by the teeth to adepth of about 10 to 25 mils during operation.

FIGS. 6-8 illustrate the pattern abradable seal 26 schematically, withFIG. 6 also illustrating the relative position of the seal 26 vis-à-visa radially opposed seal tooth 20. The seal 26 is shown as comprised ofthe base coating 46 and the patterned surface 48, the latter similar topattern 42 in FIG. 4. In the exemplary embodiment, the base abradablecoating may have a thickness of between about 15-100 mils, and thepatterned surface may have a thickness of between about and 15-100 mils(would prefer if this statement can be generalized). With a totalcoating thickness of between about and 30-200 mils. With thisarrangement, and in an exemplary embodiment where the seal is employedfor use with a shrouded bucket in the high-pressure section of a steamturbine, the cold clearance can be reduced to about 10 mils. Note thatthe “abradable coating” and the “base coating” may be the same material,and the depth or thickness of the “abradable coating” merely indicatesthe depth of the pattern itself relative to the overall coatingthickness.

In the exemplary embodiments, the stationary; pattern-abradable/abrasiveseal is used with shrouded buckets but it is not limited to thatapplication, and in fact, may be used wherever seal teeth are employedon rotating turbine components.

It is also a feature of the invention to add anti-swirl features to thepattern-abradable/abrasive seal. These features help reduceswirl/tangential flow components and thus provide better rotor dampingand improve overall turbine efficiency. For example, as illustrated inFIGS. 9-11, the anti-swirl feature takes the form of angled or slantedthree-dimensional rectangular blocks 50 that are aligned along thedownstream edge 52 of the stator shroud 54 (or stationary turbinecomponent), at an acute angle relative to an axial centerline of thestator, overlying the pattern-abradable/abrasive seal coating, i.e.,projecting radially beyond the patterned surface. With this arrangement,leakage flow entering the pattern-abradable/abrasive seal component willfirst impinge on the anti-swirl blocks 50 which will break up theswirling flow caused by the rotating buckets and create an axial leakageflow component by means of the angled gaps between the anti-swirl blocks50, before flowing around seal tooth 58 (FIG. 9). The blocks 50 may bespray-coated onto the surface 56 and built up to the desired thickness,using conventional masking techniques. Alternatively, the coatingsand/or anti-swirl features can be manufactured as removable inserts. Thematerial may be the same as the patterned surface 56 and/or the basecoating 60. As already mentioned, the base coating and patterned surfacemay likewise be of the same material. It is noted that the anti-swirlfeatures are located at a position (or positions) axially offset fromthe opposed seal tooth is that there is not contact between the sealtooth and the anti-swirl features.

Another exemplary but nonlimiting embodiment is illustrated in FIGS.12-14 where a similar row of angled, rectangular blocks 62 are alsoapplied along the upstream edge 53 of the shroud, bracketing the sealtooth. For FIGS. 12-14, reference numerals used in. FIGS. 9-11 are alsoused here to designate corresponding components. Here again, theswirling or tangential flow is broken up and the leakage flow is causedto have an axial flow component as it passes through the gaps betweenthe angled blocks 62, over the seal tooth 58 and through the gapsbetween similarly angled blocks 50.

A still further exemplary but nonlimiting embodiment is shown in FIGS.15-17 where solid annular ribs or rings (or ring segments) 64, 66 areprovided along the upstream and downstream edges 68, 70 of the patternedsurface 72 which overlies the base coating 74.

FIGS. 18-20 illustrate yet another exemplary but nonlimiting embodimentof anti-swirl elements added to a pattern-abradable seal. Here, rows ofangled, rectangular blocks are applied not only along the upstream anddownstream edges 76, 78 of the stator shroud 80, but also between themarginal rows. More specifically, marginal rows 82, 84 of blocks 86, 88,respectively, and two intermediate rows 90 and 92 of blocks 94 and 96,respectively, are applied to the patterned surface 98 overlying the basecoating 100. The height of the blocks in each row is dictated by theseal tooth height. With particular reference to FIG. 18, it may be seenthat blocks 86 and 82 are the same height as blocks 96 and 92 and bothrow interact with relatively long seal teeth 102, 104 of substantiallythe same height. Similarly, blocks 94 and 88 in rows 90 and 84,respectively, have substantially similar heights dictated by therelatively shorter seal teeth 106, 108. The swirling tangential flow isbroken up by the angled blocks and given an axial flow component but, inthis embodiment, the different heights of the seal teeth cause theleakage flow to follow an even more tortuous path in the axialdirection, leading to even greater sealing efficiency.

In this embodiment, the seal teeth engage the anti-swirl features, i.e.,the anti-swirl features also serve as seal elements, and therefore, thebase surface need not be patterned.

FIGS. 21-23 illustrate another exemplary but nonlimiting embodiment,utilizing multiple seal teeth 102, 104, 106 and 108 as in thepreviously-described embodiment, but wherein the anti-swirl featurescomprise plural rows 110, 112, 114 and 116 of circumferentiallystaggered, rectangular blocks 118, 120, 122 and 124, respectively,arranged on the pattern-abradable seal 126 (overlying the base coating128), substantially parallel to the direction of flow. The differentialheight of the blocks and the seal teeth remain as described inconnection with the embodiment illustrated in FIGS. 18-20 but here,there are no axial gaps between the rows 110, 112, 114 and 116 (compareFIGS. 18 and 21), but there are circumferential gaps between theadjacent staggered rows as plainly evident from FIGS. 22 and 23, thusproviding unobstructed axial passageways for leakage flow.

It will be appreciated that the combination ofpattern-abradable/abrasive seals and anti-swirl features is applicableto other steam turbine bucket configurations, nozzle root seals andlabyrinth packing seals. In this regard, attention is drawn to FIG. 24which is similar to FIG. 1 but wherein four seal teeth 130, 132, 134 and136 are located in axially-spaced relationship along the bucket shroudtip 138, arranged to engage opposed abradable-pattern seals 140, 142,144 and 146 on a packaging ring segment 148 as described above.

In FIG. 25, a nozzle root seal arrangement is disclosed wherein the sealteeth 150, 152, 154 and 156 are arranged to penetrate thepattern-abradable seal elements 158, 160, 162 and 164.

FIG. 26 discloses yet another embodiment where seal teeth 166, 168 and170 on the rotating component 172 are interleaved with seal teeth 174,176 and 178 on a stationary packing ring segment 180. Between thepacking ring teeth, the pattern-abradable seal elements 182, 184 and 186are applied to the surfaces of the packing ring segment 180.

It will be appreciated that any of the anti-swirl elements described inconnection with FIGS. 9-23 may be employed with the seal elements shownin FIGS. 24-26.

To demonstrate the significant reduction in tangential flow velocityachieved with the anti-swirl features described herein, FIG. 27 plotstangential velocity against the axial length of the anti-swirl blockshown, for example, in FIG. 22. It can be seen that there is a dramaticreduction in the high swirl component velocity from the inlet (orupstream) end to almost zero at the exit end of the anti-swirl feature.

It is still another feature of the invention to utilizepattern-abradable/abrasive seal coatings or inserts on surfaces axiallyupstream or downstream of the rotatable components such as theblades/buckets described above, FIG. 1, for example, illustratescoatings or inserts 190, 192 on upstream and downstream vanes or nozzles12, 14, respectively.

FIG. 24 also illustrates a pattern-abradable/abrasive coating or insert194 on a downstream, stationary component, adjacent the bucket tipshroud 13B.

By designing the pattern on the coating/insert to provide defined flowpaths, it is possible to direct the leakage flow at a favorable angle tothe adjacent rotating or stationary component.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A pattern-abradable/abrasive seal assembly for a stationary steamturbine component, the seal assembly, in use, oriented in opposition toat least one seal tooth on a rotatable steam turbine component so as toinhibit leakage flow across the seal assembly and/or guide the leakageflow in a first direction, the seal assembly comprising: an annular sealcarrier having at least one axially-oriented, annular seal surface; apattern-abradable/abrasive seal coating at least partially covering saidat least one axially-oriented, annular seal surface, saidpattern-abradable/abrasive seal coating having a pattern formed therein,adapted, in use, to face and be at least partially penetrated by the atleast one opposed seal tooth; and a plurality of anti-swirl elementsprojecting radially beyond said pattern and arranged circumferentiallyabout said at least one axially-oriented, annular seal surface.
 2. Thepattern-abradable/abrasive seal assembly of claim 1 wherein theabradable seal coating comprises a ceramic material or a metal alloy. 3.The pattern-abradable/abrasive seal assembly of claim 1 wherein saidpattern has a depth of from about 50 to 100% of a total thickness ofsaid abradable seal coating.
 4. The pattern-abradable/abrasive sealassembly of claim 1 wherein said plurality of anti-swirl elementscomprise a first plurality of substantially rectangular blocks, alignedand spaced about one circumferential edge of the said annular sealcarrier, axially spaced from said at least one seal tooth, saidrectangular blocks arranged at an acute angle relative to an axialcenterline passing through said annular seal carrier.
 5. Thepattern-abradable/abrasive seal assembly of claim 4 wherein saidplurality of anti-swirl elements further comprise a second plurality ofsubstantially rectangular blocks, aligned and spaced about an oppositecircumferential edge of said annular seal carrier, said second pluralityof said rectangular blocks arranged at substantially the same acuteangle as said first plurality of substantially rectangular blocks. 6.The pattern-abradable/abrasive seal assembly of claim 1 wherein saidplurality of anti-swirl elements comprise three or more axially-spaced,circumferential rows of substantially rectangular blocks.
 7. Thepattern-abradable/abrasive seal assembly of claim 1 wherein saidplurality of anti-swirl elements comprise plural,circumferentially-staggered rows of substantially rectangular blocks. 8.The pattern-abradable/abrasive seal assembly of claim 1 wherein saidpattern comprises a criss-cross mesh pattern.
 9. Thepattern-abradable/abrasive seal assembly of claim 1 wherein said patterncomprises a plurality of substantially rectangular brick-shapes.
 10. Thepattern-abradable/abrasive seal assembly of claim 7 wherein saidrectangular blocks are oriented in an axial direction.
 11. A stationarysteam turbine component located along a gas path comprising: a firstsurface facing an adjacent rotating steam turbine component; and a firstpattern-abradable/abrasive coating or insert having a pattern formedtherein applied to said surface wherein said pattern is designed todirect leakage flow in a predetermined direction relative to saidstationary steam turbine component.
 12. The stationary steam turbinecomponent of claim 11 wherein said stationary steam turbine componentcomprises a turbine vane or nozzle and said rotatable steam turbinecomponent comprises a turbine bucket.
 13. The stationary steam turbinecomponent of claim 12 wherein said turbine vane nozzle is locatedaxially upstream of said turbine bucket.
 14. The stationary steamturbine component of claim 12 wherein said turbine vane or nozzle islocated axially downstream of said turbine bucket.
 15. The stationarysteam turbine component of claim 12 wherein said turbine bucket isformed with a tip shroud supporting on or more radially-outwardlydirected seal teeth, and a stationary stator surface surrounding saidtip shroud is provided with a second pattern-abradable/abrasive coatingor insert facing said one or more radially outwardly directed sealteeth.
 16. The stationary steam turbine component of claim 15 andwherein said second pattern-abradable/abrasive coating includes one ormore anti-swirl features projecting radially beyond said patternabradable/abrasive coating or insert.
 17. A turbine bucket and abradableseal assembly comprising: a bucket having a tip shroud formed withplural radially-directed seal teeth; a stationary stator componentsurrounding said bucket and having plural abradable seals opposingrespective ones of said plural radially-directed seal teeth; whereineach of said plural abradable seals includes an abradable seal coatinghaving a pattern formed on a surface thereof facing a respective one ofsaid plural, radially-directed seal teeth, and at least one ananti-swirl element projecting radially beyond said pattern and arrangedto provide at least an axial component of flow across the seal assembly,said at least one anti-swirl element opposed to one of said pluralradially-directed seal teeth, and adapted to be at least partiallypenetrated thereby.
 18. The turbine bucket and abradable seal assemblyof claim 17 wherein said at least one anti-swirl element comprisesplural circumferentially-arranged rows of anti-swirl elements.
 19. Theturbine bucket and abradable seal assembly of claim 18 wherein saidplural circumferentially-arranged rows of anti-swirl elements areaxially-spaced and staggered in the circumferential direction.
 20. Theturbine bucket and abradable seal assembly of claim 18 wherein eachanti-swirl element of said plural circumferentially-arranged rows ofanti-swirl elements is arranged at an acute angle to an axis of rotationof said bucket.